Impregnated ceramic insulators and method of making same

ABSTRACT

Moisture resistant electrical insulators particularly for use in electrical connectors including a matrix of a normally porous ceramic material which is impregnated with a thermoset electrically insulating resinous composition.

United States Patent Exner 1 Sept. 12, 1972 [541 IMPREGNATED CERAMIC INSULATORS AND METHOD OF MAKING SAME [72] Inventor: William E. Exner, Elmhurst,1l1.

[73] Assignee: The Pyle-National Company, Chiqtl lf [22] Filed: Sept. 16, 1970 [21] App1.No.: 72,595

[52] U.S. Cl. ..339/176 M, 117/72, 117/123 D, 174/209, 339/278 D [51] Int. Cl. ..lI0lr 23/02, H01r 13/46 [58] Field of Search ..339/278 D, 176; 117/123 D, 117/72; 174/209, 210

[56] References Cited UNITED STATES PATENTS 3,091,750 5/1963 Long et a1 ..339/112 2,020,718 11/1935 B01 et a1 ..117/123 D 2,657,153 10/1953 Russell ..117/123 D 3,336,158 8/1967 Wada etal ..117/123 D 3,407,086 10/1968 VoisineLl ..117/123 D 3,503,822 3/1970 Turkewitsch ..1 17/72 FOREIGN PATENTS OR APPLICATIONS 294,182 4/1914 Germany ..174/209 Primary Examiner-Marvin A. Champion Assistant Examiner-Laurence J. Staab Attorney-Hil1, Shennan, Mcroni, Gross & Simpson 5 7] ABSTRACT Moisture resistant electrical insulators particularly for use in electrical connectors including a matrix of a normally porous ceramic material which is impregnated with a thermoset electrically insulating resinous composition.

7 Claims, 3 Drawing Figures 'IMPREGNATED CERAMIC INSULATORS AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION 1 Field of the Invention This invention is in the field of electrical connectors of the type in which a plurality of thin electrical contacts is enclosed by the connector, the thin, closely spaced electrical contacts extending through a ceramic insulating disc. The improvements in such structure are directed mainly to the sealing of the normally porous ceramic disc to make it resistant to humidity without detracting from its strength or without significantly increasing its dimensions.

2. Description of the Prior Art In some types of connectors, particularly miniature connectors, the individual contacts are supported within a ceramic disc in very closely spaced relation, with the separating walls between the axial passages in the disc sometimes being as thin as 0.010 inch. Such connectors are used extensively in environments containing substantial amounts of moisture and since such ceramic materials are normally porous, the bulk and surface resistance values of the material are susceptible to degradation by moisture.

Normally, porous ceramic materials used in electrical insulators are prepared for use by vitrification of the surface, or by coating with a suitable resin, or by any other surface glazing method to provide a moisture barrier. However, such surface preparations are not practical in the case of miniature connector insulation. Such insulation must be dimensionally precise with tolerances on the order of one thousandth of an inch. Conventional surface preparations inherently provide additional surface thicknesses ranging from 0.003 to 0.010 inches, and have the inherent characteristic of filleting inside corners and rounding outside corners. These characteristics destroy the dimensional accuracy required in miniature connector insulation. Furthermore, such surface preparations are susceptible to penetration by scratching, and any such penetration provides the means for moisture penetration into the body of the insulation.

SUMMARY OF THE INVENTION The present invention provides an improved insulator having a normally porous ceramic matrix and being impregnated with and coated with a heat resistant resin. In a particularly preferred form of the present invention, a silicone resin is used to impregnate the interstices of the porous ceramic matrix, as well as providing an extremely thin outer coating over the ceramic element. By proper application of the impregnant and coating materials, the increase in overall dimension of the ceramic insulator should not exceed about 0.001 inch. The silicone resin has the ability to permeate completely into the pores of the ceramic material and to become bonded tenaciously thereto. The impregnant is insoluble in water, oils and solvents to the same extent as the other components of the connector. The silicone resin, particularly, is capable of withstanding temperatures as high as those withstood by the other components and even upon thermal pyrolysis does not carbonize.

The improved insulator of the present invention usually takes the form of a ring having a large number of closely spaced axial passages therethrough which receive the electrical contacts. Ceramic discs of this type are normally siliceous or they may be of the porous clay type containing refractory materials such as zircon, alumina, sillimanite, calcined china clay, and talc. They may also be of the vitreous type composed, for example, of a mixture of clays, talc, sillimanite or other refractory material and felspar.

In accordance with the method aspects of the present invention, the normally porous ceramic body is first impregnated with a solution of a thermosetting, electrically insulating resin after which the resin is cured within the interstices of the porous matrix. Then, the impregnated matrix is coated with a surface coating of a thermosetting electrically insulating resin, which is usually the same as the resin of the impregnant, except that the solids content of the coating composition is substantially less than the solids concentration in the impregnating solution. This provides a thin outer coating on the impregnated ceramic composition which effectively seals off the surfaces without significantly increasing the outer dimensions.

The impregnating resins which can be used for the purpose of the present invention preferably include a silicone resin, either alone or in combination with a polyester resin. Other types of resins can, however, be used including such materials as phenolic resins, melamine resins, diallyl phthalate resins, polyester resins, urea resins, epoxy resins and polyimide resins.

Other objects, features and advantages of the inven' tion will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

FIG. 1 is a view partially in cross-section and partially in elevation illustrating an electrical connector employing the improved insulating material of the present invention;

FIG. 2 is an enlarged cross-sectional view taken substantially along the line IIII of FIG. 1; and

FIG. 3 is an enlarged fragmentary cross-sectional view of the impregnated ceramic, illustrating both the impregnated matrix and the surface coating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10 indicates generally an electrical connector including a receptable shell 11 having an annular flange portion 12, and a threaded end portion 13 at one end thereof. A back cap 14 is joined to the shell 11 as by means of adhesive or the like. The back cap 14 is also adhesively secured to an insulator disc 15 of the type with which the present invention is concerned. The insulator disc 15 contains a plurality of axially extending apertures 16 in each of which there extends a thin metallic pin contact 17, the latter having a headed portion 18 being tightly received within a collet 19.

As best illustrated in FIG. 3, the insulator disc 15 is composed of a porous ceramic matrix 20 having a resinous impregnant 21 completely filling the pores of the matrix, and a very thin surface coating 22 completely sealing the outer periphery of the element.

One of the particularly preferred impregnant and coating compositions for the purpose of the present invention consists of a silicone modified polyester resin composition. In the formulation of this material, about 50 parts by weight of polyester solids are combined wit 56 parts of a silicone intermediate such as Dow Corning' Z-6l88. The resulting material has a solids content of about 65 percent. The materials are reacted together in the presence of a catalyst consisting of tetraisopropyl titanate, in an amount of about 0.5 percent based upon the weight of silicone, in a solvent mixture of Cellosolve acetate and butyl alcohol. In the formulation of this material, the polyester is heated to 120 C. and then the mixture of catalyst, solvent, and one-half of the silicone intermediate is added. The mixture is then reheated to 120 C. at which time the second half of the intermediate is added. Heating to about 130 C. causes the viscosity of the solution to increase rapidly. The heating is continued until the final viscosity is between 100 and 400 centipoises at a solids content of 50 percent. The reaction is stopped by the addition of the Cellosolve acetate solvent. After the reaction mass is cooled to 100 C., or less, the butyl alcohol is then added. This procedure results in the preparation of a silicone polyester having a 50 percent solids content and an acid number of 2 to 4.

For the impregnation procedure, a sealing solution can be prepared by dispersing the polyester-silicone resin in a mixture of methanol and methyl isobutyl ketone. The solids content of this impregnating solution is usually about 24 percent by weight.

After dipping of the ceramic element in the first dip solution, which takes about a minimum of 30 minutes time, the parts are removed from the dip tank and blown with air to remove excess solution. The parts are then placed in an oven temperature of 57 C. for at least 105 minutes, and possibly as long as 2 days. Then, the parts are placed in an oven at a temperature of 205 C. for a minimum of 35 minutes so that curing of the thermosetting material takes place.

After the first cure, the impregnated part is then redipped in a second solution of the polyester-silicone resin which contains about l2.35 percent solids. This second dipping occurs for a minimum of 105 minutes. After removal from the impregnating solution, the parts are spun on a suitable fixture to remove excess resin. After drying, the parts are placed in a dilute solution of the same resin, typically containing 9.35 percent by weight solids. The parts are agitated gently in the rinse solution for approximately 1 minute, then removed from the solution and excess resin blown off in an air stream. The drying is accomplished in an oven operating at 57 C. for at least 12 hours after which the parts are placed in a 205 C. oven for 35 minutes minimum, or up to 2 days, if necessary.

The product which results is a ceramic matrix completely impregnated with the polyester silicone resins, and having a durable surface coating measuring less than 0.001 inches in thickness.

The resin impregnating and coating process of the present invention permits porous ceramic parts to be used in applications for which they were formerly unacceptable due to their inability to maintain electrical integrity in high humidity conditions. The process also seals the parts so that they may be used as a pressure barrier in arr or gas pressure systems. The parts can be disc in closely spaced relation, said disc being com posed of a normally porous ceramic matrix, the improvement comprising, a thermoset electrically insulated heat-resistant resinous composition of a given solids content impregnated within said porous ceramic matrix disc to substantially completely fill the pores thereof, and a surface coating on said disc of a thickness less than about 0.001 inch comprised of a thermoset electrically insulating heat-resistant resinous composition having a lower solids content than said given solids content.

2. The connector of claim 1 in which said resinous composition is a silicone resin.

3. The connector of claim 1 in which said resinous composition is a polyester resin.

4. The connector of claim 1 in which said resinous composition is a phenolic resin.

5. The connector of claim 1 in which said resinous composition is a melamine resin.

6. The connector of claim 1 in which said resinous composition is an epoxy resin.

7. In an electrical connector, a shell, an electrically insulating disc positioned within said shell, and a plurality of thin electrical contacts extending through said disc in closely spaced relation, said disc being composed of a normally porous ceramic matrix, the improvement comprising, a silicon modified polyester resin composition of a given solids content impregnated within said porous ceramic matrix disc to substantially completely fill the pores thereof, and a substantially uniform surface coating on said disc of a thickness less than about 0.001 inch comprised of a silicon modified polyester resin composition having a relatively lower solids content than said given solids content. 

2. The connector of claim 1 in which said resinous composition is a silicone resin.
 3. The connector of claim 1 in which said resinous composition is a polyester resin.
 4. The connector of claim 1 in which said resinous composition is a phenolic resin.
 5. The connector of claim 1 in which said resinous composition is a melamine resin.
 6. The connector of claim 1 in which said resinous composition is an epoxy resin.
 7. In an electrical connector, a shell, an electrically insulating disc positioned within said shell, and a plurality of thin electrical contacts extending through said disc in closely spaced relation, said disc being composed of a normally porous ceramic matrix, the improvement comprising, a silicon modified polyester resin composition of a given solids content impregnated within said porous ceramic matrix disc to substantially completely fill the pores thereof, and a substantially uniform surface coating on said disc of a thickness less than about 0.001 inch comprised of a silicon modified polyester resin composition having a relatively lower solids content than said given solids content. 